1. Field of the Invention
This invention relates to expanding-gate-type gate valves. More particularly, the invention relates to a gate valve having an expanding gate and including replaceable valve seat inserts in which the valve seat inserts are removably received in recesses formed in the valve body, engage the opposite faces of the expanding gate, and have a longer effective operating life.
2. Description of the Related Art
Gate valves are used in a large number of fluid flow systems for flow control purposes. A generally rectangular solid gate member is provided having a pair of spaced, parallel faces that include a through passageway that extends through the gate member from one face to the other. The through passageway is positioned adjacent one end of the gate and the gate is adapted to be moved within the gate valve body to alternately bring the through passageway into and out of registry with a flow passageway to selectively permit flow through the valve and to prevent flow through the valve. A pair of valve seats are provided within the valve body and are so positioned on opposite faces of the gate that they engage the gate faces. The valve seats are provided to prevent flow around the gate rather than through the gate.
Because of their effectiveness to control flow of fluids, gate valves are often used in oil field applications. Frequently, such valves have an expanding gate to insure zero flow through the valve when the valve is in the closed position. However, because drilling fluids that are used to facilitate the drilling process often contain gritty materials and particles, valves used in such applications are subject to considerable wear, thereby resulting in the need to frequently replace the valve seats in order not to experience excessive leakage through such valves.
One solution that has been devised to solve the wear problem has been to provide a resilient sealing ring that is retained in the face of the valve seat that faces the gate face, both to provide a wiping action on the surface of the gate, and also to physically space the metallic portion of the seat from the gate and thereby reduce the frictional wear that would otherwise result when grit or other particles find their way between the valve seat and the gate. Oftentimes the annular sealing rings, which usually are made from a polytetrafluoroethylene (Teflon) material, are held in annular recesses formed in the face of the seats, the annular recesses having inwardly facing serrations on their inner surfaces to provide gripping surfaces to aid in retaining the sealing ring in position. However, the formation of such grooves and serrations adds substantially to the cost of such seats.
In addition to the additional cost, the resilient sealing rings are often damaged in use. Frequently, pressurized fluid seeps around the ring to enter the recess, which results in an outward force tending to force the ring out of the recess. As a result the ring partially extends into the passageway in the gate and is cut by the edge of the gate passageway as the gate moves over the sealing ring during opening and closing of the gate. Consequently, pieces of the rings are severed from the ring bodies, and result in hollowed-out spaces within which particulate matter can collect and further increase the wear problem. Valve seats incorporating such annular sealing rings are shown in U.S. Pat. No. 4,376,526, which issued on Mar. 15, 1983, to John W. Freeman, and in U.S. Pat. No. 4,471,943, which issued on Sep. 18, 1984, to Norman A. Nelson.
The prior art expanding gate valves also included seats that were force fit into the valve body. In that regard, U.S. Pat. No. 2,954,960, which issued on Oct. 4, 1960, to Calvin D. Dunbar et al., and U.S. Pat. No. 4,489,918, which issued on Dec. 25, 1984, to Manmohan S. Kalsi show such fixed seats. Alternatively, seats having limited axial movement are disclosed in the Nelson U.S. Pat. No. '943 patent.
It is an object of the present invention to overcome the problems attendant with the known expanding gate valve structures.
It is another object of the present invention to provide an expanding gate valve structure in which the valve seats do not contain resilient sealing rings in the sealing faces, and are also resistant to wear.
It is a still further object of the present invention to provide a simple, relatively inexpensive, and uncomplicated valve seat that provides greater longer operating life and is easy to replace.